LATE-GLACIAL PALEOENVIRONMENT OF LAKE ALGONQUIAN SEDIMENTS NEAR CLARKSBURG, ONTARIO

Excavation below the Lake Algonquin gravel beach bar near Clarksburg, Ontario, exposed mollusc-bearing clay over a lens of plant debris. Thi s is the northernmost and most deeply buried Lake Algonquin fossil sit e found thus far in Ontario. It is the first site to provide dates fro m directly below the Algonquin beach bar. Two radiocarbon dates of abo ut 11 200 years confirm the age of isostatically transgressing Lake Al gonquin. Plant macrofossils (21 taxa), pollen (39 taxa), molluscs (12 taxa), and ostracodes (18 taxa) indicate that the climate was colder t han present by several degrees and the forest-tundra ecotone was nearb y initially but retreated northward rather quickly. Upward increases i n abundances and diversity of molluscs and ostracodes suggest it was a time of rapid migration and colonization of species.